Method and apparatus for classifying finely-divided solids carried in a gas stream



Feb. 11. 1969 R. H. STARK 3,426,893

METHOD AND APPARATUS FOR CLASSIF-YING FINELY-DIVIDED SOLIDS CARRIED IN A GAS STREAM Filed April 18, 1967 INVENTOR Roy H. Stork United States Patent 3,426,893 METHOD AND APPARATUS FOR CLASSIFY- ING FINELY-DIVIDED SOLIDS CARRIED IN A GAS STREAM Roy H. Stark, Riverside, Pa., assignor to Kennedy Van Saun Corporation, New York, N.Y., a corporation of Delaware Filed Apr. 18, 1967, Ser. No. 631,833 US. Cl. 209-3 Int. Cl. 1307b 4/04 13 Claims ABSTRACT OF THE DISCLOSURE Background of the invention The invention relates to improvements in the classification of mixtures of comminuted or finely-divided materials, such as those obtained by grinding coal, ores, cement and other materials in some sort of grinding mill sometimes swept by an air stream, or otherwise discharged into an air stream which picks up a mixture of finely-divided solid material comprised of particles of varying mesh. Such mixtures are sometimes subjected to classification in a vertically-arranged classifier from which the air stream carries the finer particles of the mixture over into a cyclone separator, in which the product is separated and from which the separated product is recovered.

In some of these known types of operations the oversize particles of material are taken out of the classifier and returned to the griding mill.

Known types of classifiers are illustrated by Niemitz Patent 2,638,217, granted May 12, 1953, and the references cited at the end of that patent. Some of the classifiers disclosed in these patents, particularly that of the Niemitz patent, are very complicated and expensive structures.

Summary of the invention The method and apparatus of the present invention provides a system for classifying and separating desirable components of a particulate solid substance or material comprising a plurality of components of different mesh carried in a gaseous medium such as air. The mixture of components is advanced in a continuously moving main stream in succession through a series of zones in an enlarged expansion zone, and using cross or through-flow air streams in each zone for stripping the fine components from the heavier or larger undesired components of the moving stream. The resulting classified desired components fluidized and entrained in air are drawn off from the expansion zone.

The cross-flow air streams are advantageously taken separately from the main air stream in advance of the expansion zone. One of the advantages of the invention is that the mixture of solid substances is carried in a continuously moving stream and stripped of fine particles as it moves along, and, therefore, avoids the use of complicated apparatus.

Another advantage is that the oversized particles are carried along in the main stream without being appreciably diverted therefrom or scattered through the apparatus. The system provides a novel procedure for controlling the quantity of air in the main air stream, in which the oversized undesirable particles are carried into the apparatus. Furthermore, the apparatus provides an arrangement by which a thin wide stream of particles is subjected to classification of the particles.

Brief description of the drawing The drawing accompanying this application discloses a single embodiment of an apparatus for carrying out the improved method.

In the drawing:

FIG. 1 is a vertical sectional view through a classifier embodying the features of the present invention and in which the improved method may be carried out;

FIG. 2 is a view taken on the line 2-2 of FIG. 1 illustrating the relative proportions of the width and thickness of the inlet channel or duct; and

FIG. 3 is a broken sectional view taken on the line 3-3 of FIG. 1 showing the relative transverse relations between the various channels and the expansion chamber.

Description of the prefenred embodiment FIG. 1 of the drawing shows the classifier 10 constructed and arranged as shown in accordance with the invention. It includes a front wall structure including an outer plate 12, the lower downwardly inclined portion of which is carried on transverse channel iron supports 14 and a concave rear wall 16. The classifier is provided with a shallow wide inlet duct 18 at the top, an outlet duct 20 at the bottom for oversize rejects and an outlet duct 22 at the top for an air stream carrying the desired product, which may be drawn by a fan through one or more cyclone separators from which the product is recovered.

The interior of the classifier is divided into a preliminary separating chamber 24 and an enlarged expansion chamber 26 separated from the chamber 24 by a wall 28. The classifier is called a vari-mesh classifier and this refers in general to the character of the product taken through the duct 22, the mesh of which may be changed or varied by utilizing a switch gate 30 fixed at the top to a pivoted shaft 32, which extends through the end Walls of the classifier and which is operable by a lever on the outside of the classifier by means of a hydraulic piston and cylinder unit or other means. The gate 30 includes a Wide rigid section 34 to the lower end of which is hinged a swingable section 36. The sections 34 and 36 extend from end wall to end Wall in chamber 26. The lower end of the section 36 is positioned by chains 38, or other means, to the back wall 16. When the lower end of the gate section 34 is swung to the right, as indicated by the dotted line positions, it decreases the size of the expansion chamber 26 and consequently increases the velocity of the air and size of the solid particles moving upwardly through that chamber and through the outlet duct 22. When very fine particles are desired, the gate 30 is kept in the full-line position shown in FIG. 1.

In carrying out the improved method and in effecting the operation of the classifier according to the invention, a thin, wide stream of air and mixture of solid particles 40, for example, from a grinding mill, is introduced into the inlet 18 through an arcuate wideshallow duct '42. The velocity of the air stream or other gaseous medium is such that the suspended solids are concentrated in its upper portion by centrifugal action, as shown in the upper part of the duct 42 and the inlet duct 18. In other words, the particles are concentrated largely on the outside of the stream in this portion of the apparatus.

As the stream enters the separating chamber 24, a considerable portion of the air, for example approximately 20% (18 to 22%), is drawn off through a wide duct 44 along with a portion of the fine material suitable for the desired product. This duct 44 is controlled by a gate 46 having a pivot shaft operable from outside the classifier. The purpose of the port or duct 44 is to draw off some of the air which would otherwise go to the expansion chamber 26, thus reducing the air quantity and velocity of the stream of air and large or heavy particles which flow through the chamber 24 and out a bottom opening 48 into the expansion chamber 26. If a relatively coarse product is desired for delivery from the expansion chamber through the duct 22 the gate 46 should be moved to close off the port 44, so that a greater proportion of the air flows on into the expansion chamber 26. At the same time the gate or wall 34 is moved to the right to effect the eventual control of the mesh of the product delivered through the outlet duct 22.

The right side of the separating chamber 24 is defined largely by successively lower gates 50, 52 and 54 associated respectively with relatively thin, Wide ducts 56, 58 and 60, comprising a part of the front wall structure located inside and supported by the wall plate 12. Secondary air from the chamber 24 is drawn off through the ducts 56, 58 and 60 along With some of the finer particles of the solids carried by the air stream and passed into the chamber 26 through successively lower outlets 61, 59 and 57. This secondary air diffuses across the chamber 24 leaving the larger particles to flow on as a continuous stream in air through the passageway 48 into the expansion chamber 26. The passageway 48 is controlled by a gate 62. The solids passing through the passageway 48 flow in succession over the outlets 61, 59 and 57 of the ducts 60, 58 and 56, which duct outlets open into the expansion chamber 26 at successively lower points.

The main stream of air and the bulk of the solid particles may be passed through the passageway 48 at considerable velocity, but in some instances, the air may be a small proportion of that delivered through the inlet 18. On the entry of the stream into the expansion chamber 26, preferably at a lower pressure than the chamber 24, there is expansion, and diffusion of the finer particles into the open space of the chamber. Secondary air and some of the finer solids are drawn off from chamber 24 through the ducts 56, 58 and 60, and these streams are discharged through 57, 59 and 61 and used to strip the solid particles flowing downwardly through the chamber 26. The air passing through the duct 56 is the cleanest air and is also the final secondary air used at the lower part of the chamber 26.

In this operation the solids flowing through the passageway 48 immediately flow over the outlet 61 and are swept by secondary air flowing therefrom around the upper edge of the duct 60, by which the finer particles are influenced to move outwardly and upwardly. From here some of the finer solids are carried to the top of the chamber 26 as product, some move horizontally and some continue downward toward the reject opening 20. Solid particles that continue downward in the chamber 26 over the outlet 59 and are swept by secondary air flowing therefrom around the upper edge of duct 58 to substantially repeat the separations taking place above. However, at this point, the expansion chamber has a smaller cross-section, which exerts a greater influence toward carrying fine solid particles upwardly. Finally, the rejects at the bottom of the chamber 26 are swept by air flowing from the outlet 57 to boost finer particles toward the product outlet 22. The cleanest secondary air taken from the upper part of the chamber 24 is used in this final stripping operation.

The controls as effected by the gates 50, 52 and 54 may be such that the air moving transversely across the chamber 24 substantially diffuses across this chamber, so that it carries only minor amounts of extremely fine particles of the stream flowing toward and through the passageway 48. The quantity of air flowing through the 60 may be varied according to tests made on the rejects delivered through the outlet 20. Cross-flow stripping air streams at successive points is desirable because the first or second cross flows may not remove all of the fine particles which are intermingled with the rejects as the main stream of the latter flows downwardly through the chamber 26.

The diffusion of air to the right across the chamber 24 is, of course, regulated in accordance with the opposite diflusion into the duct 44, in which a somewhat lower velocity is used to carry out very fine particles into the outlet 22. When the desired product may include particles of relatively large mesh, carried in the main air stream, the wall 34 is moved over to the right to decrease the size of the expansion chamber 26, and accordingly, increase the speed of upward flow of air delivered thereinto from the passageway 48 and the ducts 56, 58 and 60. Simple tests of the product delivered through the outlet 22 and of the rejects delivered through the outlet 20 may be used in determining the position of the wall 34 and the amount of stripping to be done, and therefore, the position of the gates 46, 50, 52, 54 and 62.

The improved method and classifier of the present invention may be utilized for various purposes, as pointed out above. If coal is pulverized in a mill in order to supply burners of a steam generating plant, for example with pulverized coal as fuel, the air stream and fine coal particles delivered through the outlet 22 may be sent by blowers directly to the burners. When other materials are being classified, the outlet 22 may be connected into one or more cyclone or other type of separators and recovered in accordance with conventional practices.

The classifier of the present invention may be built in various sizes according to the plant in which it is to be used. In a particular instance the classifier was designed to have a height of about 17 feet from the bottom of the outlet 20 to the top of the outlet 22, a dimension of about 10 feet across from the back wall 16 to the front wall plate 12 at about the level of the line 3-3. The dimension in the opposite direction was approximately 8 feet, which is the same for the width of the inlet 18 and the duct 42. The opposite inside dimension of the inlet 18 was about 10% inches. From this example one can readily understand the various relationships illustrated in the drawing.

1 claim:

1. In the method of classifying finely-divided solids carried in a stream of gaseous carrier medium such as air in which the stream and finely-divided solids of varying mesh are subjected to classification in an enlarged expansion zone, wherein the improvement comprises the steps of passing a main stream of gaseous medium carrying finelydivided solids of varying mesh in continuous flow into one side of the expansion zone, causing the stream of solid particles to flow downwardly and inwardly in said expansion zone toward a discharge outlet for rejected particles of relatively coarse mesh, passing a plurality of separate streams of stripping gaseous medium containing particles of relatively fine mesh in suspension respectively transversely through successive parts of the stream of solid particles flowing downwardly through the expansion zone, suspending the desired particles of relatively fine mesh of said stream of solid particles in the gaseous medium and suspended fine particles passed into the expansion zone and removing them from the upper part of the expansion zone in a stream of said gaseous medium.

2. The method as defined in claim 1, wherein portions of the gaseous medium of the main stream are separated therefrom along with fine particles in a preliminary separating zone prior to the introduction of the main stream into the expansion zone, and wherein said separated portions of the gaseous medium are utilized to provide said plurality of separate streams of the stripping gaseous medium passed into the expansion zone.

3. The method as claimed in claim 2, including diverting a further portion of the gaseous medium from various ducts 56, 58 and the main stream in said preliminary separating zone and delivering it into the stream flowing from the upper part of the expansion zone.

4. The method is claimed in claim 1, including the step of passing the main stream as a thin wide stream through an arcuate passageway and causing the particles of larger mesh carried by said stream to collect in the outer peripheral part of the stream flowing through the arcuate passageway, and thereafter delivering the particles of larger mesh into the expansion zone.

5. The method as claimed in claim 1, wherein the main stream as delivered into the expansion zone is a thin, wide stream, and wherein the plurality of separate streams of Stripping gaseous medium passed into the expansion zone are thin, wide streams.

6. In a classifier for classifying finely-divided solids carried in a stream of gaseous carrier medium including an enlarged expansion chamber in which chamber the stream of finely-divided solids of varying mesh are subjected to classification, wherein the improvement comprises means for conducting a main stream of gaseous medium carrying finely-divided solids of varying mesh in continuous flow into the upper portion at one side of the expansion chamber, means for causing the stream of solid particles to flow downwardly and inwardly in said expansion chamber, a discharge outlet for rejected solid particles at the bottom of the expansion chamber, means for directing a plurality of separate streams of stripping gaseous medium transverly respectively through successive parts of the stream of solid particles flowing downwardly through the expansion chamber to suspend the desired particles of fine mesh in the gaseous medium of said streams in the expansion chamber, and means for conducting the classified particles of fine mesh from the upper part of the expansion chamber in a stream of said gaseous medium.

7. A classifier as claimed in claim 6, including a movable wall mounted in the expansion chamber for respectively decreasing and increasing the cross-sectional area of the expansion chamber.

8. A classifier as claimed in claim 7, wherein the classifier includes an inlet passageway for admitting said main stream to the expansion chamber and in which said movable wall is located opposite said passageway.

9. A classifier as claimed in claim 8, in which said movable wall is pivoted at the upper portion of the expansion chamber near the means for conducting fine particles therefrom, said wall being swingable toward said inlet passageway and including means located generally above the inlets of said streams of gaseous stripping medium.

10. In a classifier for classifying finely-divided solids of varying mesh carried in a stream of gaseous carrier medium including an enlarged expansion chamber in which chamber the finely-divided solids of varying mesh are subject to classification, wherein the improvement comprises a preliminary separating chamber located adjacent to the expansion chamber in the classifier, means r opening into the expansion chamber for conducting successive streams of stripping gaseous medium from the preliminary separating chamber transversely through the stream of solid particles flowing downwardly through the expansion chamber to suspend the desired particles of fine mesh of said stream in the gaseous medium in the expansion chamber, and means for conducting the classified particles of fine mesh from the upper part of the expansion chamber in a stream of said gaseous medium.

11. A classifier as claimed in claim 10, wherein the inlets to said ducts opening into the preliminary separating chamber are at successively lhigher points, and wherein the duct opening into said separating chamber at the highest point discharges into the expansion chamber at the lowest point of all the ducts.

12. A classifier as claimed in claim 10, including a control gate for each of said ducts for controlling the flow of gaseous medium from said preliminary separating chamber into the expansion chamber.

13. A classifier as claimed in claim 10, wherein the means for conducting said main stream and said ducts connecting the preliminary separating chamber with the expansion chamber are wide, thin ducts.

References Cited UNITED STATES PATENTS 2,214,434 9/1940 Nelms 209- 2,777,576 l/ 1957 Stevenson 209136 2,850,162 9/1958 Widmer 209-143 X 3,240,335 3/1966 Vandenhoeck 209154 X FOREIGN PATENTS 560,450 4/1944 Great Britain.

TIM R. MILES, Primary Examiner.

US. Cl. X.R. 209-143, 154, 135 

